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51.
Min Cheng 《辐射效应与固体损伤》2013,168(11-12):1083-1089
ABSTRACTThe EPR g factors g// and g⊥ for the tetragonal (CrO4)3? impurity center in ZrSiO4: Cr5+ crystal are studied from the high-order perturbation formulas based on the two-mechanism (the crystal field and charge-transfer mechanisms) model. The studies indicate that differing from the tetragonally-elongated host (SiO4)4- tetrahedron, the dominant defect structure of the substitutional (CrO4)3? tetrahedron is tetragonally- compressed with the ground state |dz2 due to the Jahn-Teller distortion. Furthermore, the agreement of g factors between calculation and experiment requires a small admixture of the first excited state |dx2?y2 to the ground state |dz2 due to the vibrational motion of ligands, which leads a compressed (CrO4)3? tetrahedron to become a twinkling elongated one, These results are discussed. 相似文献
52.
Bucur V 《Ultrasonics》2005,43(4):237-239
The aim of this study is to assess wood quality of standing trees with ultrasonic velocity methods. The ultrasonic techniques currently used are: scattering based techniques that use travel time and other wave parameters for measuring the elastic constants of wood, and ultrasonic tomographic imaging techniques which seek to provide a high resolution picture of the defect. Scattering based techniques were firstly used as nondestructive techniques with increment cores of 5 mm diameter. On these specimens measurements with bulk waves--longitudinal and shear were used to detect the influence of sylvicultural treatment (pruning) on wood quality and also to detect defects (slope of grain, wavy figures). High resolution imaging techniques were developed for imaging abnormalities induced by biological attacks of fungi or insects in standing trees. In this case, ultrasonic tomography refers to cross-sectional imaging of trees from data collected by illuminating the tree from different directions. Ultrasonic images were reconstructed from the time of flight. The images were reconstructed from 120 measurements in situ and through the bark with direct transmission technique, using 1 MHz transducers. The resolution is 5 cm. 相似文献
53.
Adam Rudziński Anna Tyszka-Zawadzka Paweł Szczepański 《Optical and Quantum Electronics》2007,39(4-6):501-510
The aim of this paper is to present the analysis of influence of defects in 1D photonic crystal (PC) on the density of states
and simultaneously spontaneous emission, in both spatial and frequency domains. In our investigations we use an analytic model
of 1D PC with defects. Our analysis reveals how presence of a defect causes a defect mode to appear. We show that a defect
in 1D PC has local character, being negligible in regions of PC situated far from the defected elementary cell. We also analyze
the effect of multiple defects, which lead to photonic band gap splitting. 相似文献
54.
Zhiyun Zhang Chonggao Bao Wenjing YaoShengqiang Ma Lili ZhangShuzeng Hou 《Superlattices and Microstructures》2011
Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by RF magnetron sputtering method under different substrate temperatures. The microstructural, electrical and optical properties of AZO films were investigated in a wide temperature range from room temperature up to 350 °C by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), Hall measurement, and UV–visible meter. The nature of AZO films is polycrystalline thin films with hexagonal wurtzite structure and a preferred orientation along c-axis. The crystallinity and surface morphologies of the films are strongly dependent on the growth temperature, which in turn exerts a great effect on microstructural, electrical and optical properties of the AZO films. The atomic arrangement of AZO film having an wurtzite structure was indeed identified by the HRTEM as well as the Selected Area Electron Diffraction (SAED). The defect density of AZO film was investigated by HRTEM. The film deposited at 100 °C exhibited the relatively well crystallinity and the lowest resistivity of 3.6 × 10−4 Ω cm. The average transmission of AZO films in the visible range is all over 85%. More importantly, the low-resistance and high-transmittance AZO film was also prepared at a low temperature of 100 °C. 相似文献
55.
The CASTEP calculations based on the density function theory (DFT) have been carried out in studying magnetic properties of C-doped ZnO crystal. The long-range ferromagnetism (FM) can be attributed to coupling between C energy levels. We also investigate effects of oxygen vacancies and nitrogen impurities on FM properties. It is obvious that oxygen vacancies are unfavorable to stabilize the FM. However, nitrogen impurities can enhance FM coupling, which indicates that hole-carriers play a crucial role in the observed FM behavior. In addition, we also analyze strain effect on FM of C-doped ZnO. 相似文献
56.
Nonlinear Elastic Wave Spectroscopy (NEWS) relies on the activation of defects by wave energy that propagates through the medium. In general, the response of activated defects will not scale linearly with the excitation amplitude, and the resulting nonlinear signatures can be identified and used for quality inspection. The efficiency of NEWS based inspection methods is therefore intrinsically linked to the locally deposited activation energy at the defect zone and the ability to generate nonlinear signatures that exceed the noise level of acquisition. Time Reversal techniques allow focusing of high levels of energy in small areas, and are consequently very useful for the local activation of defected zones. In this report, numerical simulations are reported showing the potential of a combination consisting of dual energy reciprocal Time Reversal and nonlinearity filtering using the Scaling Subtraction Method. The method is applied to the detection of planar near-surface defects parallel to the surface in a 2D domain. The results are evaluated for sweep excitation at different frequency ranges; for point-like receiver as well as extended transducers, and for in-plane as well as out-of-plane focusing. The observable nonlinear response at the surface is linked to an effective nonlinearity within the medium based on the defect geometry and the distribution of the local stresses. 相似文献
57.
Rare earth doped BaZrO3 is one of most promising proton conducting oxides as it has high proton conductivity and sound chemical stability. Sintering aids such as ZnO, however, should be incorporated in order to improve poor sinterability. In this study, the effects of adding ZnO on proton conductivity of Yb-doped BaZrO3 (BZYb) were investigated. From the electrical conductivities measured under various water vapor pressures, concentration and mobility of the proton were obtained. Proton mobility of BZYb with ZnO (BZYb-Zn) was smaller than that of BZYb while hydration enthalpy of BZYb-Zn was more negative than that of BZYb. 相似文献
58.
The chemomechanical properties and microstructural stability of nanocrystalline PrxCe1 − xO2 − δ solid solutions are studied as a function of temperature by in situ X-ray diffraction measurements under oxidizing conditions at P(O2) ~ 200 mbar. The chemical expansion coefficient of nanocrystalline powder specimens, operative at intermediate temperatures during which Pr4+ is reduced to Pr3+, is found to be similar to that obtained for coarse-grained PrxCe1 − xO2 − δ. This is contrary to reports regarding variation of physical and chemical properties with crystallite size. The thermal expansion coefficient, measured under conditions for which PrxCe1 − xO2 − δ is highly oxygen deficient, was found to be greater than that measured for fully oxidized PrxCe1 − xO2 − δ, with potential sources of these changes discussed. Moreover, the microstructure of nanocrystalline PrxCe1 − xO2 − δ is observed to have excellent stability at working temperatures below 800 °C, enabled by the inherent microstrain in the structure, highlighting the potential application of this material for solid state electrochemical devices. 相似文献
59.
60.
Takashi Nakamura Keiji Yashiro Kazuhisa Sato Junichiro Mizusaki 《Journal of solid state chemistry》2009,182(5):1121-299
In order to elucidate the relation between thermodynamic quantities, the defect structure, and the defect equilibrium in La2−xSrxNiO4+δ, statistical thermodynamic calculation is carried out and calculated results are compared to those obtained from experimental data. Partial molar enthalpy of oxygen and partial molar entropy of oxygen are obtained from δ-P(O2)-T relation by using Gibbs-Helmholtz equation. Statistical thermodynamic model is derived from defect equilibrium models proposed before by authors, localized electron model and delocalized electron model which could well explain the variation of oxygen content of La2−xSrxNiO4+δ. Although assumed defect species and their equilibrium are different, the results of thermodynamic calculation by localized electron model and delocalized electron model show minor difference. Calculated results by the both models agree with the thermodynamic quantities obtained from oxygen nonstoichiometry of La2−xSrxNiO4+δ. 相似文献